Control system



NOV. 5, 1940. w rn 2,220,748

CONTROL SYSTEM Filed Jan. 12, 1940 2 Sheets-Sheet 1 Fig. I. Y 11- 6 A33 16 c an. L

Fig. 2.

FLUX

TEME'.

Inventor'- Max A. Whi in His Attorney.

Nov. 5; 1940.

M. A. WHlTlNG CONTROL SYSTEM 2 Sheets-Sheet 2 Filed Jan. 12, 1940 imawnu CUT RETURN w m fl w a 'mm t h b nwJA n m m M w a H b RETURN Patented Nov. 5, 1940 UNITED STATES CONTROL SYSTEM Max A. Whiting, Schenectady, N. Y., minor to General Electric Company, a corporation of New York Application January 12, 1940, Serial No. 313,581

9 Claims.

This invention relates to control systems, more particularly to reversing control systems, and it has for an object the provision of a simple, re-

liable, and improved control system of this character. I

More specifically, the invention relates to reversing control systems in which the excitation of a field winding is to unc' z'go frequency reversal, and in which suitable current limiting de- 10 vices such as rheostats are provided for controlling the maximum current in each direction. For

example, one rheostat will be set to allow the maximum current to fiow that is desired for one direction, and the other will be set for the maxi l5 mum current that is to flow in the reverse direction. Suitable reversing switching means are provided for connecting the winding to a source for excitation first in one direction and then in I the other and with the proper rheostat in circuit. During the reversal of connections, that is, after disconnection of the winding from the source and prior to its reconnection in the reverse directiom'it has been customary to connect the terminals of the winding to a discharge resistor in which the magnetic stored energy of the winding was discharged and dissipated. Under such conditions the initial rate of decay of the flux when the winding is disconnected is proportional to the amount of current flowing in-the winding when it is disconnected from the source, 1.. e., during the first instant of discharge. Obviously, if the initial rate of decay of fiux from the maximum is not excessively great,,-the initial rates of decay from one-halfmaximum or one-fourth maximum are much less than the maximum permissible.

When the maximum economy of time. is important, for example, when it is desired to obtain the largest possible number of reversals per minute between narrowly separated limits of travel, a decay of generator flux which begins at an unnecessarily slow rate results in waste of time and is therefore a handicap. Accordingly, a further and more specific object of this invention is the provisioncf means for causingthe decay of the field fiux during each reversal to begin at a high rate, preferably at a rate close to the maximum permissible. I H

In carrying the invention into effect in one form thereof, a dynamoelectric machine having a field winding is operatively associated with a reversing drive such asthe drive for a planer equipment. The field winding is arranged to be connected to a source of supply, and a variable current limiting device, such as a variable resistor is provided for limiting the excitation of the field winding to desired values. Means, such for example as switching devices, are provided for selectively including this current limiting device in circuit with the field winding in accordance with its direction of excitation, and switch- 5 'ing means areprovided for connecting the field winding to its source of excitation and for subsequently reversing the connections to the source so that'the excitation is reversed. During the reversal, a discharge circuit is established for the gr; field winding which includes the current limiting device used to limit the current just prior to the reversal.

For a better and more complete understanding oi the invention, reference should now be had to 15 the following specification and to the accompanying drawings in which Fig, l is a simple schematic diagram of a circuit useful in explaining the principle of the invention, and Fig. 2 is a chart of characteristic curves of the rates of rise and decay 20 of flux of the field winding of the circuit of Fig. 1. and Fig. 3 is a simple schematic diagram of an application embodying the invention.

In Fig. 1 the field winding ll of a Ward-Leonard generator is arranged to be connected to a 25 source of excitation H and I2. A permanent series resistor l3 andan adjustable resistor or rheostat i4 areincluded in series circuit relation with the .field .winding,'and a fixed discharge resistor I! is provided to be connected in parallel 30 with the field winding to affect its discharge and to, dissipate the stored energy. A double throw switch servesato complete and to interrupt the connections of the fieldwinding Hi to the source and. to establish the discharge circuit. It may he 35 assumed that the inductance L of the winding Hi remains constant although in practice this is not strictly true. 3

Let the rheostat ll be turned to zero resistance and let-switch l6 remain closed to discharge re- 40 sistor-cl! until the .fiux of generator field III has become zero. Then close switch I8 to resistor l3. Let the time constant of the circuit as now constituted be L/r 'asplotted in Fig. 2, in which r is the resistanceof the generator field l0 plus the, resistance of resistor IS. The rise of the generator magnetic fiux will then be in accordance with curve a. At time b, let switch l6 be quickly opened from resistor l3 and closed to resistor i5, and let the resistance of resistor I5 be equal to 50 the resistance of resistor 13. Then L/r for the new circuit condition will be as shown in Fig. 2 and the decay of the generator fiux will be in accordance with curve I), d, I, 9.

Now, in Fig. 1, turn in enough of rheostat H to 55 75 termined low value [adjustable esisto v 165;: lists th r n? ied? Even wi h;

7 attract their cpr'e "and-closetheir'eontacts,

1 a [thesejc'on' ct ar -closes: by their main limit the generator excitation to one-half maximum. Upon closure'oi switch IE to resistor #23,

the time constant L/r will be one-half its former value. The initial rise of generator flux will begin as rapidly as before and will follow curve '0'. After steady-state has been obtained, at one-half maximum excitation; =let switch it be quickly opened-from resistor l3 and -closed to resistor-i5.

The time constant L/r is now the same as originally and the decay of flux beginning at d proj ceeds along" curve 1, f, g. The initial rate of so:

decay; at d, is only one-half the intial' ratejatlb when the decay is from full field,

Similarly, t rheostat m has'bee zaojustd to limit theexcitation to one-fourth niaximumfthe' initial decay of flux at point I isvery slow, only one-fourth of vthe initial rate at b when'de'cayingi from maximum, As previously pointed out when onomy of time is rmpomntucr from anadjustable'voltaigelgeiieraton.Ziwhich is 3 y 7 suitable driving means, suchaais a nduotion motor'lno't' shownlrC0n= Yfin. PX- M} ie are i 3"when pick'e'd up: connects the generator r i8 may "be ii'sed-,'- .ii' adesiresi, eries I vvi'tl'i the -generator: field. sister i 'havingl 't'Wo'L-niieut r rheostat' enerates cu a 'ovable'c'ontact Etitfofthe return rheostat a voltagel {The pullof thesejcoils is insufficient to mitt is, the auxiliary coils: aintainftiie fco'ntacts "closed operating "coils: 3 een- 51 1' W 1 i until the generator voltage decays to a am 24 t6 t e sourceaza zs for excitehe diredtion, andwcontactor; es similarlyior' the "retum direction. An,

the. following detailed desqnp Y may; arly V side '25-. or the source.

sponse to energization. After relay 3? has-been mliary; coils l 3% and i sfrespecre energized I iromthe generator.

but

predeassures The operating coils of field directional contactors 28 and-2i are connected in series with the main operating coils 30b and 3), respectively, of the selective contactors 3E and 3!. A resistor 38 is included in circuit with these coils and it is controlled-by a contactor 86 whose operating coil 3 3s is energized from the generator voltage. Whenthe-generator voltage islower than a predetermined valuegcontactor 34 is closed and resistor 33 is short-circuited and one of each of the pairs of contactors can be closed. When the generator voltage is above a predetermined value,

contactor 3li'is open. Contactors such as 23 and '--;2'ias normally designed requirea substantially greatercurrent for picking up, i. e. closing, than is necessary for holding closed after hav ingi been piclged'upgasis well known in the art.

Resistor 331s of a resistance value low enough not to"--ca;use drop-out of contactors 23 and .30 01 :81. and fifiif introduced into circuit H after pick- .sqth t'.. int s nd-f l (if resistance is'high enough hile the" contactors are a it" will prevent; pick-up .uswheh anyiof" these confrom occurring; ll

taetors is dropped out, it 'cannotbe closed'until the generator Voltage hasjdecayed to-a' predeterrsmi ned litre same: Thusjcontactorfltj piotects t fluggingflthejfild exce at relatively .,;values oil generatoryvoltagei wi h lponteetors are, dropped out f' coiitacts- 2 3,}; and 21s lease, and the generator n w; at is connected dischargeflcircuit. 'j

- sen ments a an e hat her h t r enstatorthelfreturn rheostat selectively is in ii" during the principalpart of the discharge.

So ng retu'rn push buttonssfi and iit'a're'oper- If button 3,5; is' pressed' "momentaxily, 3T3,- picks' up and starts the planer in 1 the 'Lvntomaticfoperation isfinterrupted an'd'is not 1 1 s nned until push button 3510i" :Sffifis pressed. 1

with ther regbmg understandingfiof the elesmears-(a d their 7 organization; the operation thereystem; tself mllreadily be understood from Assume: relay 3? to be open and "the -planer platen 38 to; be in any positionsuchthat the an; is; is between switches is and an.

To start'in the cu direction, the-pushbutton is depressed. This energizes relay 3? The circuit is tracedirom side 25 of :the'source fnrough conductor 3Q, contacts of limit switch i-ieonductor lEi, lower contacts of "cut button concluctor ii, coil of automatic relay 8? to Relay-.31 closes in re= picked up, push button 35 may getreleased because the vcurrentthrough resistor 32 is sufficient to maintain relay 3? picked fup,. alt hough insuficientto pick it up. In the closed position oi relay 3?, the operatingcoilsof contactors and 3!? are now energized. The circuit is traced from 1 side. 25 of the source to conductor se s before, *thence through the'upper contacts of relay 371, normally closed contacts of "return button 36,

lower interlock contacts of return" contactor 2?,

ei bontactoifs "2a and 27 are' 'provided the purpose of the present-invention; the

upon relays for initiating automaticfopdirection where'upon automatic-operation v t ensues between. the 'llniit i'switches fl 8 and" 2t.

-j imilarly if buttonafi is pressed, relay 3? is similarly-picked up; butiautomatic operation begins with x a niovenient injthe I retufrf direction. a t-mome tary. opening 'oripush batten so, the

coil of cut" contactor 23, coil 30s of selective contactor 30, resistor 33 to the side 23 of the supply source. Contactor 23 picks up and connects the generator field winding 24 to the source for energization in the cut" direction, and selective contactor 30, in picking up, short-circiuts the portion 29r29c of the resistor and leaves section z9s--29d constituting the cut" rheostat in circuit. The field circuit is traced from side 25 of the source through conductor 43, upper contacts of out contactor section 233-294 of resistor 29, field winding 24, lower contacts 2120f return contactor, thence through a portion 0! adjustable resistor 23 to the side 23 of the supply source. The lower contacts of contactor 23 are opened when the contactor picks up thereby pro-- viding an additional interruption of the circuit extension from coil of contactor 21. Thus, when cut" push button 35 is released, the contactor operation is not interfered with.

When the generator voltage rises to a sunlciently high value, contactor 34 will pick up and insert resistor 33 in circuit with the coils of con-' tactors 23, 21, 33 and 3|. This prevents contactors 21 and 3| from picking up until the generator voltage again drops to a predetermined low value. 1

8:. opens limit switch 20, this causes cut" contactor 23 to drop out. At the instant that cut contactor 23 drops out, its lower auxiliary contact closes and completes a circuit for the operating coils of return contactor 21 and selective contactor 3|. However, since the generator voltage is still high, contactor 34 remains picked up and the resistor 33 reduces the energization of these coils so that the contactors 21 and 3| do not pick up. Actually, both cut" and return contactors remain open briefiy and provide .a 40 discharge circuit for the generator field 24. This discharge circuit extends from the upper terminal of field winding 24 through upper closed contacts 21a of return contactor 21, through conductor 44, portion of resistor 28, contacts 23. of 45 cut contactor, contacts of selective contactor 30, cut rheostat 29a29d to lower terminal of field winding 24. It will be noted that the dis charge circuit does not include the return" rheostat 29d-v29c which has been and now is 50 short-circuited by the contacts of selective contactor 30.

Assume that when the contactor 23 was closed to connect field winding 24 to the source, the cut rheostat was turned in sumciently to limit 55 the generator voltage to one-fourth maximum. When the contactor 23 closed, the fiux oi the generator field increased in accordance with curve e of Fig. 2 until the maximum 8 max. was reached. When the contactor 23 opened to dis- 60 connect the field winding 24 from the source and connected it in a discharge circuit including the cut rheostat, the fiux decayed along the curve f-k. It will be noted that the initial rate of decay is much greater than it would have been 65 in the conventional discharge circuit arrangement which would have been along the curve fg.

The increased rate of decay which results from making the resistance of the discharge circuit 70 inversely proportional to the current can be explained as follows:

During the rise of the field from zero, the circuit equation is:

in which E is the constant bus exciting voltage, 1 is the field current, 1' is the total resistance of the field circuit, N is the number of turns of the field winding, and

isthe self-induced voltage of the field. first instant i is zero, and

Ndd:

For the discharge the circuit equation is:

At the first instant oi discharge i= max. It is assumed here that the resistanceot the discharge circuit has been made equal to the value of 1' which determined the value of t max.

Thereiore, at the first instant of discharge (mi. r=E. Therefore,

At the sufliciently low value, selective contactor 30 drops out and contactor 34 also drops out and closes its contacts to short-circuit resistor 33. As a re sult selective contactor 3| and return contactor 21 are energized. The circuit is readily traced from side 25 of the source through contacts of limit switch l3, conductor 45, lower contacts of relay 31. normally closed contacts of cut push button 35, conductor 46, lower auxiliary contacts of cut contactor 23, operating coil of return contactor 21, operating coil 3| 0! selective contactor 3|, contacts of contactor 34 to side 26 oil the source.

Contactor 3| closes and short-circuits portion 29h-29e of resistor 29, and return" contactor 21 closes and connects field winding 24 to the source forexcitation in the return direction. The circuit is traced irom side 25 of the source through upper contacts of return contactor, field winding 24, return rheostat 2317-494, resistor 23 to side 26 oi the source. a

' During this time, dog 13. is to the right of the pivot of limit switch 23. Accordingly, this limit switch has remained open. When return" contactor 21 picks up, its auxiliary contact opens the circuit extension of the coils of cut contactor 23 and selective contactor 30 at a second place. Accordingly, when the platen moves toward the left, away from switch 20, the reclosure of limit switch 20 is unable to energize the coils of contactors 23 and 30. Hence the operation of the return movement is not interfered with. When limit switch It is opened by dog |8., the reversal from return to cut. takes place in a similar manner to that described for the reversal from out to return". During this reversal, however, the "return rheostat Mir-294 is included in the discharge circuit and thus the field is again discharged through a circuit of resistance properly related to the initial value of the field to insure initial high rate 0! fiux decay in accordance with the principles set forth hereinbetore.

Although in accordance with the provisions of the patent statutes, this invention is described as embodied in concrete form and the principle of the invention has been explained together with the best mode in which it is now contemplated applying that principle, it will be understood that the elements and connections shown and described are merely illustrative and that the invention is not limited thereto, since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of this invention or from the scope of the annexed claims.

What I claim as new and desire to secure by Letters Patent 01 the United States-is:

1. A control system for a machinery combination and the like characterized by repeated cyclic reversals comprising in combination, a dynamo electric machine operatively associated with said equipment, said machine having a field winding,

a current limiting device operatively associated with said field winding, means for selectively rendering said current limiting device active in accordance with the polarity of the magnetism of said field winding to limit the current fiowing in said field winding, and means for reversing the current flowing in said winding 'when said current limiting device is active, and means for establishing a discharge circuit for said field winding during said reversal including said current limiting device.

2. A control system for a machinery combina-.

tion and the like characterized by repeated cyclic reversals comprising in combination, a dynamoelectric machine operatively' associated with said equipment, said machine having a field winding, a. pair of current limiting devices'operatively associated with said field winding, means for selectively rendering said current limiting devices active in accordance with the polarity of the magnetism of said field winding to limit the current of said winding, means for reversing the current fiowing in said field winding, and means for establishing a selective discharge circuit for said field winding during a reversal including the current limiting device active during the operation immediately preceding said reversal.

3. A reversing control system for planer equip: ments and the like comprising in -combination, a dynamoelectric machine operatively associated with said equipment, said machine having a field winding, a pair of current limiting devices operatively associated with said field winding, switching means for selectively rendering one of said current limiting devices active in ac-- cordance with the polarity of the magnetism of said field winding, and switching means for reversing the direction of current fiowing in said field winding and for cooperating with said selective switching means to establish a discharge circuit for said field winding during a reversal including the current iimiting device active during the operation immediately preceding said reversal.

e. A reversing control system for planer equipments and the like having a reciprocating member comprising an adjustable voltage generator having a field winding, a motor supplied from said generator for driving said equipment, a current limiting device operatively associated with said field winding, switching means responsive to actuation by said equipment for selectively rendering said current limiting device active in accordance with the direction of motion of said reciprocating member, and reversing switching winding at predetermined points in the travel of said reciprocating member and for establishing a discharge circuit for said field winding during said reversals, the discharge circuit established following the stroke of said member in which said current limiting device was. active including said current limiting device.

, 5. A reversing control for planers and the like having a reciprocating member comprising an adjustable voltage generator provided. with a field winding, a motor supplied from saidcgenerator for driving said equipment, a pair of adjustable value current limiting devices adapted to be included in circuit with said field winding, reversing switching mechanism responsive to operation of said reciprocating member for reversing the direction of the current in said field winding thereby to effect reversal of the rotation of said motor and reversal of the movement of said member, and switching means responsive to operation of said reversing switching mechanism for selectively including said current limiting devices in said field circuit at the beginning of each stroke of said reciprocating member, said reversing switching mechanism serving to establish a discharge circuit for said field winding during the period of current reversal therein including the current limiting device active in said field circuit during the stroke of said member immediately preceding said reversal.

6. A reversing control system for planer equipment and the like having a reciprocating member comprising an adjustable voltage generator provided with a field winding, a motor supplied from said generator for driving said equipment, a current limiting device adapted to be included in circuit with said field winding, reversing switching mechanism actuated by said reciprocating member for reversing the direction of current fiow in said winding thereby to effect reversal of the direction of rotation of said motor and the direction of motion of said member, switching means responsive to actuation by sa'd driven equipment for selectively including said current limiting device in circuit with said field winding during energization of said winding in one direction, said reversing switching mechanism serving to establish a discharge circuit for said field winding including said current limiting device during each of said field current reversals immediately following an operation with said current limiting device in circuit with said -=field winding.

'7. A reversing control system for planer equipments and the like having a reciprocating member comprising an adjustable voltage generator provided with a field winding, a motor supplied from said generator for driving said equipment, a pair of current limiting devices adapted to be included in circuit with said field winding, reversing switching mechanism actuated by said reciprocating member for reversing the direction of current flow in said winding thereby to eiiect reversal of the direction of rotation of said motor and the direction of motion of-said member, switching means responsive to actuation by said member for selectively including said current limiting devices in circuit with said field winding in accordance with the direction of said reciprocating member said reversing switching mechanism serving during each of said reversals to establish a discharge circuit for said field winding including the current limiting device. active during the immediately peceding stroke of said member, and means responsive" to the generator voltage for preventing interruption of said discharge circuit until the field of said generator has decayed to a predetermined low value.

8. A reversing control system for planer equipments and the like having a member having a forward stroke and a reverse stroke, an adjustable voltage generator provided with a field winding, an electric motor, supplied from said generator for driving said member, a. pair of variable current limiting devices adapted to be connected in circuit with said field winding thereby to determine the speeds of said forward and reverse strokes, reversing switching mechanism responsive to actuation by said member for interrupting the circuit of said field winding and reversing the flow of current therein, switching mechanism actuated by said equipment for selectively connecting said current limiting devices in circuit with said field winding at the beginning of said strokes, and means responsive to the voltage of said generator for preventing the reversal of current flowin said field winding until said voltage has decreased to a predetermined low value;

9. A reversing control system for planer equippredetermined low value.

ment and the like having a reciprocating member comprising an adjustable voltage generator having a field winding, a motor supplied from said generator for driving said equipment, a pair of adjustable current limiting devices adapted to be connected in circuit with said field winding to control the speed of said motor, means responsive to actuation by said equipment for selectively connecting said current limiting devices in said field circuit so as to provide one speed of said motor for one stroke of said member and a different speed of said motor for the reverse stroke of said member, means for interrupting said generator field circuit at the end of one of said stokes and establishing a discharge circuit for said winding including the current limiting device active during the stroke immediately preceding said circuit interruption and for reversing the direction of current supplied to said winding, and means responsive to said generator voltage for preventing said reversal of current now and the actuation of said selective means until said generator voltage has decayed to a 

